I simply tried to use the firebase anonymous login catching the app activity. I enabled the login function in firebase console as well.
I created the following small function calling the firebase instance and get the signInAnonymously() method:

Yep, that’s annoying indeed. I guess you could try posting the offending code (most of it). Are we even sure the problem is with signInAnonymously()? Sorry if I cannot be more helpful atm (btw I have little experience with Dart/Flutter, so maybe some better help will come!). In the meantime, for learning purpose, I’m going to build a proof of concept app just to accomplish the anonymous Firebase login. Will let you know it I got something working out of it.